This invention relates to an improved ballast for a fluorescent lamp.
Conventional ballasts for fluorescent lamps are usually positioned within a ballast case comprised of a flat base portion and a case or cover portion secured thereto. The conventional ballasts normally include a core and coil subassembly mounted on one end of the base portion with the terminations of the coils extending therefrom. Conventionally, the layers of windings are separated by insulating material such as Kraft paper or the like. The use of paper insulation material between the layers often results in a higher operating temperature for the core and coil subassembly thereby effectively reducing the life of the ballast. The core and coil subassembly, after assembly, is normally impregnated with an asphalt wax material. The core and coil subassembly is then preferably positioned in the case so that the assembly is spaced from the top surface of the case and the sides of the ballast case for heat and sound insulation purposes, but the construction of the prior art core and coil subassembly makes such a feat extremely difficult. A capacitor/resistor subassembly is normally mounted in the other end of the case portion and usually comprises at least one capacitor and at least one resistor. Such a subassembly is sometimes referred to as a component subassembly. During the manufacture of the ballast, the leads or terminals of the capacitor(s) and resistor(s) are electrically connected to predetermined coil terminations. Elongated, flexible, external leads are also electrically connected, during the manufacturing process, to predetermined coil terminations. The total subassembly is then encased in an asphalt, silica sand potting compound. The base portion is then positioned over the ballast components and secured to the case portion with the flexible leads extending outwardly from the case. The external leads are subsequently electrically connected to leads or terminals in the lamp fixture.
The above-described ballasts, although generally satisfactory in operation, suffer some drawbacks or disadvantages. One disadvantage of the prior art ballasts is that different lamp manufacturers require leads of different lengths thereby requiring the ballast manufacturer to produce, and inventory, ballasts having various lead lengths. Further, each individual manufacturer may require various length leads to accommodate various lamp fixtures.
A further disadvantage of the prior art ballasts is that the external leads, which extend from the ballast, often interfere with other assembly operations. Yet another disadvantage is that the conventional ballast is not easily replaced by the end user should the ballast fail. Still another disadvantage is that the conventional ballast does not lend itself to potential modular product line extensions.